In the book they're there for about two days. Night falls and Maggie and Boston watch over(And presumably sleep some as well, I would think they'd be too tired to stay up all night) Ludger after they cut off his hand. The next morning they eat some berries and drink water. It's still daytime when they leave Cocytus, that would be two days and one night. They're just there for a day in the game since it never becomes night.